CB tops and manual Gain radar technique may prevent unpleasant surprises

[Centaurus]

QF severe turbulence encounter last year.
AO-2009-029 (http://www.atsb.gov.au/publications/investigation_reports/2009/aair/ao-2009-029.aspx)


Hit a CB top at night. There was no mention in the report of gain control use by the crew. Useful hint from radar manuals is to use manual gain control at max setting at high altitudes. This produces more radar power (3000 percent is the figure quoted) and CB tops of ice crystals can often be detected as a slight echo. However if gain control is in auto mode the tops may not show up at high altitudes. Once the very small echo of the ice crystals in the CB are seen on the radar screen (usually at 40-60 miles depending on tilt), the actual extent of the CB is readily seen by lowering the tilt with gain in auto. Good way to prove the theory is to practice this technique in the clear on isolated CB's. In one Pacific airline I flew with on 737's this technique worked well and saved us grief at night or IMC.

[Capn Bloggs]

Agree. In my experience, Manual Gain is the least used, least understood but most valuable feature of a weather radar.

[sleeve of wizard]

You may have heard the term: Antenna Gain
This term is somewhat misleading. It sounds as though the microwave energy enters the antenna and is somehow increased before leaving it.
That interpretation of Antenna Gain are incorrect!
The term Antenna Gain describes how much the energy leaving the antenna is focused into a particular direction.

[Capn Bloggs]

This is the gain I'm talking about:

http://i521.photobucket.com/albums/w334/capnbloggs/Capture1.gif

[Yobbo]

You are right, I have been doing it since the early seventies. I always figured the auto gain was as good as the bloke in the shop who set the auto gain.

[sleeve of wizard]

www.gapan.org/ruth-documents/study-papers/Weather Radar.pdf

[Centaurus]

The term Antenna Gain describes how much the energy leaving the antenna is focused into a particular direction.

Extracts from "Your Guide to Weather Radar" published by Rockwell Collins.
"The ability to adjust the gain control during weather detection modes provides some advantages in weather detection at the shorter ranges. Specifically, aircraft operating at high altitudes run a greater risk of encountering low reflectivity targets such as ice crystals. Adjusting the gain to provide maximum detection will aid in locating areas of low reflectivity targets.

By increasing the system gain, the pilot can effectively broaden the beam width of the transmitted signal (within the first 50 nm) to produce returns from targets that might have been otherwsie over-scanned. Once again, judicious use of the tilt and gain controls to discover the extent of nearby targets is recommended".
............................................................ ................................

[blueloo]

I would say from my experience that 95% of QF crews use MAX nearly all the time above 20000'. CAL is recommended below during terminal manoeuvring.


...but max can be pretty useless at times with ice crystals and some build ups no matter how much you scan below (or above).

[drop bear ten]

I know- we need to get some ex Ansett blokes on loan to Qantas to teach them how to use the radar..................................:p

[*Lancer*]

Centaurus, why assume the radar wasn't in MAX already? In 10 years with QF, I can't recall a single time it wasn't the 'default' cruise setting.

[flightleader]

I would like to add that max gain should be used in conjuction with some tilt manipulation to give a pilot best understanding of the weather ahead.

In the early 90's, The A330 radar is so useless that what should be red showed up as scatted greed dots. So, we have to repeatedly tilt it down to minus 8 the move it up a notch every sweep. Using simple 1-in-60 rules, we learn to read the cloud and manage to make a smarter guess of where is the top of the nasty bit where anything on top of that should be ice crystals. That help to decide how much to avoid or what can go through. Those monsters sitting over Indonesian airspace gave many good practices.

Used the same method in the B737 and B777. Works even better as these radars are more accurate.

[Kangaroo Court]

Use the same technique in corporate world now, where we spend more time in the mid 40's. Remember to tilt down to actually see anything.

[flightleader]

Good one. I'm sure you're a good manager,SGM or CEO.

[Centaurus]

Centaurus, why assume the radar wasn't in MAX already?

Speculation perhaps - but is it possible the author of the ATSB report was unaware of the choice of variable gain to seek CB tops? This could explain its absence from the report.

[maui]

Centaurus

I Know your background and acknowledge your wide experience. I would however suggest that your advice in this area is not appropriate to some more modern radar units.

The CAL (calibrated) gain setting yields the most accurate correlation

of color levels (black, green, yellow and red) with actual rainfall rates
and their corresponding thunderstorm threat levels.

CAL gain is the recommended gain position for normal operation.
Figure 4-38 shows a radar display with gain set to CAL.


The above exerpt is from the Collins WXR2100 manual.

I can't tell you how frustrated I get sitting next to guys who, lacking an understanding of advances in the radar world, apply procedures that are outdated and inappropriate to the equipment they are using, and end up diverting around returns that are either innocuous or below them.

Proffer advice by all means, but may I suggest you qualify it.

Maui

[nitpicker330]

I hardly ever use man gain on the 330, 777, 737 or 744. We were taught from day 1 what maui said above and I agree with him.:ok:

That's not to say I don't switch to man every now and then when the situation warrants further investigation. Including using low gain in high rainfall areas whilst down low in the Terminal area.

Constant use of tilt and range is a must.

I very rarely see the FO or SO with 320 nm range and 1 down tilt on a dark night over the Pacific anymore, but I used to.:=

[Offchocks]

I carried a couple of technical types from one of the radar manufacturers a couple of years ago. They were investigating that with the radar in auto, why CBs did not show up that well whilst flying over the Pacific. They came to the conclusion that the radars were calibrated for North American CBs which are apparently wetter.
Perhaps I'm just a luddite because I still use manual with the appropriate tilt/gain for the selected range................ it works well for me!

[Centaurus]

I would however suggest that your advice in this area is not appropriate to some more modern radar units.

I am sure you are right. But not all aircraft are fortunate enough to be so equipped with (for example) the Collins WXR-2100 MultiScan tm Fully Automatic Radar. The original post was intended to be helpful to those who may not have operated such advanced technology. Despite its sophistication, the WXR-2100 operator's guide does however provide useful information to those situations where variable gain is available.

[nitpicker330]

offchocks. They came to the conclusion that the radars were calibrated for North American CBs which are apparently wetter.

The same happened with the new modern ( sic ) radar on the 777-300ER that was introduced by SQ in 2007. The Honeywell RDR4000 had to be re-calibrated to suit the rest of the world conditions after they discovered it couldn't see shi* outside N.A.:D

And after 2 years using it I was not really that impressed........Give me a tilt any day thanks.

[Capt Fathom]

The Collins Manual (http://www.smartcockpit.com/data/pdfs/flightops/aircraft/Collins_WXR-2100_Operator%27s_Guide.pdf) is here.

The first part of the manual is specific to the 2100 radar itself.
The rest is about weather radar and weather in general, and operating tips.

[teresa green]

Spot on Bloggs, always used it, from early seventies.

[nitpicker330]

So Teresa, have you had much experience with a "Modern Radar" or only the original black/yellow types in the 9 and 72?

See, I've used the old stuff and the new and the newer new !! and I can tell you we don't use the gain that much anymore, in fact it's not recommended by Honeywell as the rainfall level colours are no longer calibrated to mean much.......Just like maui said above The CAL (calibrated) gain setting yields the most accurate correlation

of color levels (black, green, yellow and red) with actual rainfall rates
and their corresponding thunderstorm threat levels.


CAL gain is the recommended gain position for normal operation.
Figure 4-38 shows a radar display with gain set to CAL.

[Capt Fathom]

from early seventies

Those old phosphorous tubes were a bitch, and without a hood, were practically useless in daylight! Easy to see once you inside a CB though! :E

[nitpicker330]

yeah, the old Stevie Wonder Radar!!

Monocrome wasn't it called?

Black background with a yellow picture.

used it on the 737-200's a while back.

[BalusKaptan]

"around returns.....or below them" you say.
That seems to imply you are happy to fly over them, well not when I'm flying thank you very much. Another Crew from the company I work for tried that, cleared the highest top they estimated by a minimum of 6000' plus and the result...27 broken limbs down the back.

[molsie]

Having operated the 737NG radar for the last 8 years, I am in no doubt that the CAL ( calibrated ) gain position is next to useless at best, and positively dangerous at worst - on many occasions in the CAL position, a massive CB can be visually identified ahead, and either nothing shows up on the radar at all, or just a patch of green - it is not until you are within 50 or so miles of the CB that it then changes to yellow and then changes to red as you are about to enter it - with the gain control set to max, the radar appears to pick up the CB as it should - my advice to my FOs for years now has been to always start off with the gain control in max, and once it has picked up the CBs, adjust it as you get closer and in accordance with a bit of common sense - one of our major airlines has been wondering why they have had so many lighting strikes over the years - I suspect that this may have something to do with it.

[A37575]

a massive CB can be visually identified ahead, and either nothing shows up on the radar at all, or just a patch of green - it is not until you are within 50 or so miles of the CB that it then changes to yellow and then changes to red

Many years ago we had a similar problem with one of the 737-200's in our fleet of three aircraft. Visual big CB and nothing on radar until 40 miles. We would write up the defect but it was always ground tested Serviceable. One day I took a photo of large CB and another photo of the radar screen and sent it to Bendix in USA the radar manufacturer. Their reply was a real eye-opener. They said the problem was water had leaked either through tiny pin size holes in the radome or through defective seals. Either way, when the aircraft was at high altitude the water had frozen on the inside of the radome and attenuated the radar beam - meaning the range was drastically reduced. On descent to warmer air, the ice would melt and radar efficiency was back to normal. That is why the technicians were unable to fault the radar during ground tests,.

Bendix said the fix was to remove the radome and bake it in a special oven until all moisture in the radome was evaporated. Then examine the radome for damage to the skin and repair it. It worked fine after that. Usually if radar is playing up it is a servicing problem - not a radar design problem.

[maui]

BalusKaptan

I agree with you. I too would not fly over a red return. Those that I was referring to are yellow or green, which with modern, multiscan, fully automatic gear, are generally pretty innocuous.

By that I am not advocating flying through all yellow, but if it is a choice of a 50 mile diversion or the possibility of a short period of nil to light turbulence, I will not hesitate to take the yellow. Green is not even worth discussing. Multiscan systems show far more than previous units, and oftentimes the systems are overly sensitive. To hike up the gain only makes them moreso. Where the gain is useful is to give advance warning by picking up lighter returns at distance, but is not terribly viable as an avoidance tool.

Old methods were valid on older systems, they are not valid on the newer gear. I reckon the manufacturer knows a helluva lot more about radar/interpretation, than I ever will, so I am comfortable using the system the way the designers intended.

Hence my request of Centaurus that he qualify his observations, they do not necessarily apply the newer gear that some of us have at our disposal. One dosen't fly an A330 the way we used to fly Austers, so why would we not adopt the same philosophy to the use of other type of modern equipment.

Maui

[BalusKaptan]

Maui,

Yes, I agree with that generally. I would look at the surrounding area when contemplating penetrating a yellow area, try and assess whether it is going to stay yellow, width, height etc or whether it may still be developing. Don't want to commit to penetrating it briefly just to have it turn red at the last minute. I'm sure we have all observed, during daylight, a yellow return that when looking out the window is still in the growth stage that over a period of 5 - 10 minutes adds several thousand feet and starts discharging and as I are deviating around it turns red on the radar.

[By George]

I am afraid to say I have to agree with Mr 'Molsie' I don't have the same radar as a 'NG', don't have 'Cal', but have gain control in 'Auto' or 'Max'. 'Auto' is supposed to optimize antenna sensitivity but sometimes misses a 'dry' or decaying cell. We also have a 'Man' or 'Auto' tilt function. (744). While the base mode in cruise is 'Auto' with 0.7 degrees nose down (in 'auto' tilt) I always have a look around in manual tilt and 'Max' changing the range as well. At the risk of stating the obvious I also like to turn down the lights and look out the window to get a feel for the sky. Use all the functions and keep looking around. I'm not keen on plowing through the 'yellow' either, it puts waves in my cofee.